The present invention relates generally to a fifth wheel/upper coupler assembly for coupling a truck tractor to a semi-trailer, and more particularly to an improved self-lubricating plate for use with a trailer bearing plate and a tractor fifth wheel.
Conventionally, truck tractors have been coupled to a semi-trailer by a coupling device commonly referred to as a xe2x80x9cfifth wheelxe2x80x9d. Accordingly, the truck tractor has a xe2x80x9cfifth wheelxe2x80x9d comprising a substantially round flat plate positioned in a substantially horizontal plane to form a tractor bearing surface. The semi-trailer includes a kingpin extending downwardly to locate and seat with the locking mechanism in the fifth wheel of the tractor. The trailer further includes a trailer bearing surface to match the tractor bearing surface. Once coupled, the tractor and trailer can pivot about the kingpin to permit the truck and trailer to articulate when turning. Because the tractor bearing plate necessarily bears a large portion of the trailer weight, much friction between the two bearing surfaces is developed. This friction adversely affects vehicle handling, increases tire wear, fatigues the driver, impairs safety and causes premature wear and damage to the truck and trailer chassis and their related components.
To reduce this friction, a lubricant such as grease has been placed between the truck tractor and semi-trailer upper coupler assembly. However, it is difficult to maintain a satisfactory layer of grease between the two bearing surfaces, thus requiring the grease to be often replenished. In addition, grease is environmentally unfriendly and very messy, attracts dirt and falls from the tractor to the road surface, thus becoming a hazard to vehicles. Further, as the grease dissipates, the handling and performance characteristics of the truck tractor and semi-trailer deteriorate such that oversteer is experienced creating an unsafe condition. Too often, grease is not utilized as required.
To eliminate the need for a layer of grease, ball and roller bearings have been utilized to permit the tractor bearing surface itself to rotate. However such coupling devices are relatively complex, expensive, heavy, difficult to maintain and commercially unacceptable.
Others have replaced the layer of grease with a substrate having a low coefficient of friction, such as Teflon(copyright) or various plastics, secured as a cover to the tractor bearing surface. Commonly owned U.S. Pat. No. 5,066,035 discloses a mechanically mounted, rotatable disk produced from a polymeric material to reduce friction. U.S. Pat. No. 4,121,853 to McKay and U.S. Pat. No. 4,805,926 to Mamery disclose an anti-friction layer that is mechanically fixed to a bearing plate. And, U.S. Pat. No. 4,457,531 to Hxc3xcnger teaches a mechanically fixed, anti-friction layer attached to a tractor""s fifth wheel.
The problems associated with mechanically attached, anti-friction layers include difficulty in retrofitting, peeling or warping by the anti-friction layer, and once the layer experiences some wear the metal devices used to attach the layers come into direct contact with the metal fifth wheel causing a great deal of friction. Furthermore, replacement of the layer is a costly, time consuming procedure.
Additionally, when pulling an empty trailer, the trailer bearing surface tends to bounce on the tractor bearing surface. This vibration is transmitted into the tractor cab, further adding to the fatigue and discomfort of the driver. Likewise, metal fatigue to the truck tractor and semi-trailer increases.
The friction also leads to wear on the kingpin. While other components of the trailer bearing are lubricated, the kingpin experiences wear from the pulling and turning by the tractor. The kingpin is often difficult to replace because it is welded to the bearing surface and typically located in a place which is difficult or impossible to reach.
Furthermore, pulling, turning, and changing directions exert a great deal of force on the trailer bearing. Under the force of the loaded trailer and the tractor, the trailer bearing surface experiences premature wear requiring expensive replacement of the bearing surface.
The present invention is provided to solve the problems stated herein as well as other problems.
In accordance with the invention, a novel trailer plate assembly for semi-trailers has been developed for a truck tractor fifth wheel. The trailer bearing plate assembly comprises a self-lubricating plate fixedly attached to a housing by a chemical attachment means. The self-lubricating plate includes a perimeter surface terminating with a chamfer. A contact surface of the disk self-lubricating plate has a precision surface finish on the order of about 250 microns. This facilitates the holding of the chemical attachment means on an outer surface of the housing. The self-lubricating plate is preferably formed from an ultra-high molecular weight polyethylene plastic such as Tivar(copyright). A Tivar(copyright) disk or rectangular plate having a thickness of the order of 0.125xe2x80x3 has been found to work satisfactorily. The self-lubricating plate includes a centrally located hole to permit a kingpin to extend therethrough.
The chemical attachment means is an adhesive backing such as Adhesive FasTape #8345 or Adhesive FasTape #1191UHA (ultra high adhesive) manufactured by Avery Dennison or a liquid adhesive such as Loctite(copyright) 401 or Loctite(copyright) 4471. The contact surface of the self-lubricating plate is primed with a commercially available primer such as Loctite(copyright) 770. The chemical attachment means is then applied to the contact surface of the self-lubricating plate, and the self-lubricating plate is chemically fixed to the outer surface of the housing.
In addition, a front bar is mounted to the outer surface of the housing. The front bar is generally produced from steel rod and is welded directly to the outer surface of the housing. The front bar acts as a barrier between the self-lubricating plate and the tractor""s fifth wheel. With this arrangement, the tractor""s fifth wheel contacts the front bar prior to contacting the self-lubricating plate. Thus, the front bar prevents the tractor""s fifth wheel from xe2x80x9cgrabbingxe2x80x9d or peeling the leading edge of the self-lubricating plate from the outer surface of the housing.
The present invention may be retro-fitted to any existing semi-trailer or provided as an original equipment feature. Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.